Locking transfer cases for an all-wheel drive system or systems with part-time four-wheel drive, in which a locking or coupling function for activating one or more drive wheels comprises a clutch designed as a multi-disk clutch, are known from practice. Actuation of the clutch takes place by means of an electric motor, which acts, for example, via a gear designed as a spur gear upon a gear segment ring which, in turn, is connected to a spindle of a drive converter device.
A spindle nut, which is arranged on the spindle, is rotatably fixed in such a transfer case and is adjusted axially during a rotational motion of the spindle, in accordance with a pitch of a thread of the spindle. As a function of the direction of rotation of the electric motor, the clutch is opened or closed via the axial motion of the spindle nut.
The electric motor is hereby designed as a direct-current motor with brushes, which is combined with an electromagnetic brake in order to allow the electric motor to be shut off during extended closure times of the clutch, thus relieving it. This means that the electromagnetic brake keeps the clutch in a desired state without continuing to energize the electric motor. This prevents a so-called baking of the brushes in the traditionally employed direct-current motors that contain brushes during an extended operation without rotational movement or in a tight rotational angle area of the electric motor.
The disadvantage, however, is that the additional electromagnetic brake increases the spatial requirements of a transfer case and raises the manufacturing costs of the transfer case undesirably.
It is, therefore, the aim of the present invention to provide a transfer case, which has low space requirements and is characterized by low production costs.